The present invention relates to a method of producing an optical module in which an optical semiconductor device of a package structure and optical parts such as a lens or the like are center-aligned with each other and held by a housing. More specifically, the present invention relates to a method of producing an optical module which comprises the steps of: applying an ultraviolet-or-heat-curable resin onto a joint portion between an optical semiconductor device and a housing; irradiating the resin at the joint portion with ultraviolet rays; and heating the resin at the joint portion to fix the optical semiconductor device to the housing.
An optical module is a device in which an optical semiconductor device (for example, a semiconductor light-emitting device such as a laser diode or the like, or a semiconductor light-detecting device such as a photodiode or the like) and optical parts (such as a lens, an optical fiber ferrule or the like) are center-aligned with each other and held. For example, an optical module used in the field of optical communication is constituted by a structure which comprises an optical semiconductor device, a lens, and a housing for holding the optical semiconductor device and the lens and for fittingly holding a ferrule of a mating optical plug and in which, when the optical plug is connected, the optical semiconductor device is optically coupled with an optical fiber in the ferrule through the lens.
A spherical lens is widely used as a lens to be incorporated in such an optical module because of its advantages that a highly accurate product can be obtained easily only by mechanical processing and hence can be produced at a low cost, and that the lens has no directionality so that it is not required to adjust the direction when the lens is to be mounted in an optical module and the assembling of the optical module is facilitated. An aspherical lens, a gradient index rod lens, or the like, may be also used. Although a metal housing was widely used as the housing for holding the optical semiconductor device and the lens, a resin housing is widely used recently from the point of view of excellent workability and cost saving because of its advantage that the lens can be insert-molded in the housing or can be held by a plurality of claw-like protrusions. A structure in which a device body is sealed with a metal cap type package is generally widely used as the optical semiconductor device.
To produce such an optical module, generally, an optical semiconductor device, a lens and a fiber are center-aligned to have optically optimal positional relations and then the optical semiconductor device is fixed to a housing containing the lens. When, for example, a laser diode is used as the optical semiconductor device, the optical semiconductor device is fixed to the housing in the position where the intensity of output light taken out from the operated laser diode through the optical fiber is maximized. It is therefore necessary to prevent lowering of optical coupling efficiency due to displacement of parts when the housing and the optical semiconductor device are fixed. A method requiring a long heating time and a method accompanying mechanical impact are not desirable.
Therefore, when the housing is made of a metal, an YAG laser-welding method, or the like, is used as a typical fixation technique. When the housing is made of a resin, a method of curing a heat-curable resin such as an epoxy resin by high-frequency induction heating (see JP-A-2000-91642), or the like, is used.
The method of curing a heat-curable resin by high-frequency induction heating is excellent in the advantage that joining can be completed in a short time. There is however a problem that local temperature rising due to high-frequency induction heating is high.
Although a method using an ultraviolet-curable adhesive agent for adhesion in seconds may be hence conceived, the ultraviolet-curable adhesive agent is generally low in adhesive strength and it cannot be said that the ultraviolet-curable adhesive agent has good weather resistance. Moreover, the adhesive agent applied cannot be entirely irradiated with ultraviolet rays (portions shaded by the housing and the optical semiconductor device package are generated). Hence, portions flowing into the inside of the housing are kept uncured. There is a risk that the uncured adhesive agent may flow or fly to contaminate the front surface of the lens or the optical semiconductor device. It is hence difficult to use this method.
An object of the present invention is to provide a method of producing an optical module in which a housing and an optical semiconductor device of a package structure can be assembled in sufficient adhesive strength, high accuracy and good workability.
The present invention provides a method of producing an optical module in which with respect to a housing having an optical part received therein, an optical semiconductor device of a package structure is center-aligned to be positioned on an optical axis of the optical part and attached to the housing. The optical module is assembled through the method according to the present invention comprising the steps of: applying an ultraviolet-or-heat-curable resin onto a joint surface between the housing and the optical semiconductor device, and curing the ultraviolet-or-heat-curable resin by external irradiation with ultraviolet rays in a condition that the optical axis of the optical semiconductor device is center-aligned and joined with that of the optical part in the housing to thereby temporarily fix the optical semiconductor device to the housing; and heating the ultraviolet-or-heat-curable resin to complementarily cure non-irradiated portions of the ultraviolet-or-heat-curable resin.
The xe2x80x9cultraviolet-or-heat-curable resinxe2x80x9d used in the present invention has a function of being cured by either one of the actions of ultraviolet-ray irradiation and heating. In this respect, the xe2x80x9cultraviolet-or-heat-curable resinxe2x80x9d is different from a so-called xe2x80x9cultraviolet-and-heat-curable resinxe2x80x9d. For example, an epoxy resin containing both a heat-active cationic catalyst and an ultraviolet-active cationic catalyst is used as the xe2x80x9cultraviolet-or-heat-curable resinxe2x80x9d.
Examples of the optical part received in the housing are a lens, an optical fiber ferrule, and so on. The housing may exclusively have a structure that a lens is built in. Or the housing may have a structure that a ferrule of a counter optical plug is fittingly held as well as a lens is built in. In the latter case, the optical semiconductor device of the package structure is center-aligned so as to be positioned on an optical axis of the lens and the ferrule, by which the housing and the optical semiconductor device are fixed to each other. The method according to the present invention can be applied also to a small-size optical module in which the optical semiconductor device is directly bonded to a ferrule bore. For example, the housing is made of an opaque resin. Typically, the optical semiconductor device has a metal cap type package structure.
When externally irradiated with ultraviolet rays, a large part of the ultraviolet-or-heat-curable resin applied is cured by irradiation with the ultraviolet rays. In this step, the housing and the optical semiconductor device are temporarily fixed to each other while they are in a center-aligned state. Hence, even in the case where the temporarily fixed optical module is taken out from a retention jig for ultraviolet-ray irradiation, there is no risk that the center-aligned state may be collapsed. A part of the ultraviolet-or-heat-curable resin is not irradiated with ultraviolet rays because the part is shaded by the housing, the optical semiconductor device package, or the like. Hence, the part of the ultraviolet-or-heat-curable resin is uncured. The uncured part of the ultraviolet-or-heat-curable resin is, however, complementarily cured by heating after the ultraviolet-ray irradiation. In this manner, the whole of the ultraviolet-or-heat-curable resin is entirely cured, so that the housing and the optical semiconductor device are fixed to each other in a center-aligned state.
In accordance with the composition and characteristic of the ultraviolet-or-heat-curable resin or in accordance with the environment of use of the optical module, or the like, a sufficient effect may be obtained by fixation with the ultraviolet-or-heat-curable resin alone. On the other hand, when weather resistance becomes an issue, there may be used a method of forming a protective film on the outer surface of the ultraviolet-or-heat-curable resin. As will be described later, the more preferable method is, however, to provide a heat-curable resin on the outer surface side of the ultraviolet-or-heat-curable resin to thereby reinforce adhesion.
The present disclosure relates to the subject matter contained in Japanese patent application No. 2000-207438 (filed on Jul. 7, 2000), which is expressly incorporated herein by reference in its entirety.